Numerous processes are known for the preparation of toners, such as, for example, emulsion aggregation processes. Such toner preparation processes are illustrated in a number of patents, such as U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, 5,346,797, 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,593,807, 5,650,255, 5,650,256, 5,501,935, 5,945,245 and 6,582,873, the disclosures of which are incorporated herein by reference in their entirety. In these methods, the toners are formed chemically in situ and do not require known pulverization and/or classification methods.
Waxes are added to toner formulations in order to aid toner release from the fuser roll during fusing, particularly in low oil or oil-less fuser designs, and to help release of the fused image document from the fuser roll. That is, waxes are added to prevent the fused image document from curling around the fuser roll. In addition, waxes are added to the toner formulations in order to reduce the occurrence of stripper finger marks, such as scratch marks, changes in image gloss and the like, on the fused images, where stripper fingers aid the removal of fused image documents from fuser roll. Furthermore, waxes in toner formulations aid in the prevention of document offset where fused images on documents in contact over a prolonged period of time or at elevated temperatures may be undesirably transferred from one document to another. In addition, examples of wax containing toners include U.S. Pat. Nos. 5,482,812, 5,688,325, 5,994,020, 6,210,853 and 6,294,606, the disclosures of which are incorporated herein by reference in their entireties. For emulsion aggregation toners, for example styrene-acrylate emulsion aggregation toners, linear polyethylene waxes such as POLYWAX® 725 (available from Baker Petrolite), are useful. Conventional toners may contain and/or require a high amount of wax loading in order to achieve desirable levels of toner release. When wax is added to such toners in the bulk, and wax is substantially equally distributed throughout the toner volume, the resulting toners may contain and/or require a high amount of wax loading in order to achieve desirable levels of toner release. The high wax content of these toners can greatly increase the unit manufacturing cost of the said toners.
A number of approaches have been considered to reducing this cost including reduction of the overall bulk amount of wax added to the toner formulation. When the overall bulk wax content is lowered, the amount of wax at the toner surface is decreased, and the toner release properties, the stripper finger performance, and document offset properties of the toner composition are adversely affected. Microscopic examination of fused toners on paper has shown that there is no significant wax movement or migration from the bulk of the toner toward the surface. Therefore, it is conceivable that for fusing performance where wax is needed at the surface of the fused image, the only “useful” wax will be wax that is located near the toner surface, that is, contained in the toner shell.
Therefore, what is still needed is an improved process for forming toner particles with lower wax content, thereby improving the economic feasibility of the process, but having acceptable toner release properties, stripper finger performance and document offset properties.